NEW CONCORDIA — A downtown nightclub was destroyed by an explosion shortly after closing, sending emergency crews racing into the entertainment district and giving nearby business owners an unexpected morning of broken glass, blocked streets and insurance-related curiosity.

Authorities initially described the blast as a possible gas explosion. The explanation quickly spread through the neighborhood, where another theory — an insurance scheme — proved considerably more popular.

“I’ve smelled gas before,” said a convenience store employee two doors down. “Usually it doesn’t sound like the building declared war.”

The club had attracted a large late-night crowd and employed multiple security workers. Witnesses said police officers had been seen outside the business on previous nights speaking casually with security personnel.

City inspectors have not said whether the property had recent gas-line violations, and officials would not discuss the business’s insurance coverage.

For neighboring merchants, the immediate concern is simpler: When will the street reopen, and who pays for the damage?

Investigators have also not explained why a supposedly routine gas explosion has produced such an unusually heavy police presence.